It has become increasingly common to provide sewage pumpout stations for boats at docks. In such installations a pumpout pump is provide which is connected up to a sewage holding tank (typically of plastic) in the boat, and quickly pumps all of the sewage out of the tank. Most commercial pumps for these pumpout stations have a capacity of up to about 40 gallons per minute (151 liters per minute), although capacities of as high as 170 liters per minute may be expected in the future. When such pumps are operated, it is difficult for the pump operator to know exactly when all the sewage has been pumped out of the holding tank, and the pump may stay in operation for a significant period of time, often up to about 30 seconds, after the tank has already been emptied. It has been recognized that this can exert a substantial strain on the holding tank, and can result in damage to the tank, or an implosion. Damage to the tank may result in leakage of sewage into the environment, obviously a highly undesirable event.
In co-pending application Ser. No. 08/717,904 filed Sep. 23, 1996 (the disclosure of which is incorporated by reference herein) a number of different techniques are described by which damage to the tank as set forth above can be avoided by the provision of various constructions of vacuum relief means. According to the present invention another form of such vacuum relief means is provided which also prevents excess negative pressure inside a holding tank while being pumped out. However the vacuum relief valve assembly according to the present invention opens at about two to three inches of water, as opposed to about 13 inches of water which is typical of the structures illustrated in co-pending application Ser. No. 08/717,904. Also the valve assembly according to the present invention substantially prevents a "spitting" effect which is caused by impacts on the holding tank when full. Other relief valves often allow liquid to exit the valve when the tank is full and impacted with a 10-g load; the valve assembly according to the present invention substantially prevents this from occurring. The valve assembly according to the present invention is capable of providing sufficient air flow into the holding tank so that if the holding tank is emptied by a 170 liter per minute pump remaining in operation for 30 seconds after the plastic holding tank has been emptied, no damage to the holding tank ensues.
According to one aspect of the present invention a boat assembly is provided comprising the following components: A boat hull defining an interior boat volume. A toilet within the interior boat volume. A sewage holding tank operatively connected to the toilet, and also within the interior boat volume, the tank having an inside. An outlet conduit from the holding tank, and including a dockside pumpout fitting. An indicator of the fullness of the holding tank at at least one level of fullness thereof. A gas vent from the holding tank. And a vacuum relief valve assembly for the holding tank to prevent adverse consequences associated with a vacuum condition in the tank. the valve assembly comprising a valve body surface operatively connected to the tank and having a plurality of openings formed therein, and a flexible material diaphragm covering the openings adjacent the inside of the tank, and uncovering openings to allow air flow therethrough substantially only when a vacuum condition exists inside the tank.
The vacuum relief valve assembly is preferably constructed and configured so that the opening when the vacuum inside the holding tank is as low as about 2-5 inches of water (e.g. about 2-3 inches of water) and substantially prevents the "spitting" effect. The valve assembly also preferably comprises the support element which acts to releasably hold the flexible material diaphragm into a position covering the openings. Preferably both the diaphragm and the support element are substantially circular disks with the support disk having a diameter less than that of the diaphragm disk. A fastener assembly, such as a nut, bolt, and washer, is preferably provided to hold the disks in operative association with the valve body surface.
The valve assembly may also comprise a splash protector which is mounted to the valve body on the opposite side from the disks as the openings. The plurality of openings comprises a plurality of openings of at least two different cross sectional areas including smaller cross sectional area openings around the periphery of the valve body. Preferably, the smaller cross sectional area openings are circular, and the difference in diameter between the diaphragm and the support disk is approximately equal to the radius of the small openings.
The diaphragm is preferably of an elastomeric material having a shore A durometer of about 50-70 (e.g. about 60) and a thickness of about 0.055-0.075 inches. Preferably, the support disk comprises, or is equivalent to, a polypropylene disk having a thickness of between about 0.010-0.020 inches. The diaphragm preferably has a diameter of between about 1.85-2.05 inches, and the polypropylene disk preferably has a diameter of between about 1.65-1.95 inches.
According to another aspect of the present invention a sewage holding tank assembly is provided comprising the following components: A plastic sewage holding tank having a top and a bottom, a hollow interior, and an exterior. An outlet conduit from the holding tank and including a dockside pumpout fitting. A vent for the holding tank, adjacent the top thereof for allowing passage of gas under pressure from the tank to the exterior thereof. An inlet conduit for feeding sewage into the holding tank. And a vent check valve assembly mounted to the holding tank top for allowing passage of air from exterior of the tank to the interior of the tank when a significant vacuum condition exists within the tank, the valve assembly comprising a valve body surface operatively connected to the tank and having a plurality of openings formed therein, and a flexible material diaphragm covering the openings adjacent the inside of the tank, and uncovering openings to allow air flow therethrough substantially only when a vacuum condition exists inside the tank.
The valve assembly is mounted to the holding tank by a peripheral upper lip on the valve body, substantially all of the valve body disposed within the tank hollow interior. Other details of the valve assembly are preferably as described above.
According to yet another aspect of the present invention a valve assembly per se, which acts as a vacuum relief device, is provided. The valve assembly comprises the following elements: A valve body comprising a tubular plastic element having an open top (first end) and an open bottom (second end), a valve body surface disposed between the top and bottom and having a plurality of openings formed therein. An elastomeric material valve disk having a substantially circular configuration covering the opening adjacent the second end of the valve body. A flexible support disk of relatively stiff material engaging the valve disk and releasably holding the valve disk in a position covering the openings. And a fastener assembly for releasably holding the valve disk and the support disk entrapped within the valve body surface. The support disk preferably has a diameter about 85-96% that of the valve disk element. The other details of the valve assembly may be as described above.
It is the primary object of the present invention to provide a simple and effective vacuum relief, vent check, valve assembly, which is particularly advantageous for use with sewage holding tanks, such as on boats. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.